The newly painted city trucks had a hopeful slogan: "Philly's traffic lights are all turning green."

But, no, there will still be red lights, and drivers will still have to stop for them.

While they're waiting, perhaps they can take comfort from the fact that the new traffic signals are saving the city electricity. And money.

Mayor Nutter and a bevy of officials were at 52d and Chestnut Streets Monday, cheering on Streets Department workers as they began replacing 55,000 incandescent green and yellow traffic signals with energy-saving light-emitting diode (LED) arrays.

Half of the $6 million for the project came from a federal Department of Energy grant, the other half from Peco Energy. The lights are expected to conserve enough energy to power 700 homes and save the city $1 million a year in electric costs.

"This partnership is good for public safety, good for the environment, and," Nutter said, "in these tough economic times, it's certainly good for the city's pocketbook."

Peco president and chief executive officer Denis O'Brien said the lights would have the same environmental effect as planting 14,000 trees or not driving 14 million miles.

The focus Monday was on yellows and greens because red LED signals were installed in the 1990s, when red was the only color available using the emerging technology. But 27,000 of those aging lights will be replaced as part of the new project.

When the six-month switchover is complete, the 85,000 signals at all 2,900 intersections in the city will be LED fixtures.

How can you tell the difference? With LED signals, the light appears as small dots rather than an overall glow.